While loops in MATLAB - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of a simple while loop

What is the output of this MATLAB code?

MATLAB

i = 1;
while i <= 3
    disp(i)
    i = i + 1;
end

A

2
3
4

B

1
2
3
4

C

1
2
3

D

1
2

💡 Hint

The loop runs while i is less than or equal to 3, increasing i by 1 each time.

The loop starts with i=1 and prints i. It increments i by 1 each time until i becomes 4, which stops the loop. So it prints 1, 2, and 3.

❓ Predict Output

intermediate

Sum calculation using while loop

What is the value of variable sum after running this code?

MATLAB

sum = 0;
i = 1;
while i <= 5
    sum = sum + i;
    i = i + 1;
end

A 15

B 10

C 5

D 0

💡 Hint

The loop adds numbers from 1 to 5 to sum.

The loop adds 1 + 2 + 3 + 4 + 5 = 15 to sum.

🔧 Debug

advanced

Identify the error in this while loop

What error does this MATLAB code produce when run?

MATLAB

i = 1;
while i < 5
    disp(i)
    % missing increment of i
end

A Syntax error: missing end statement

B Infinite loop (program never stops)

C Runtime error: variable i undefined

D Outputs numbers 1 to 4 then stops

💡 Hint

Check if the loop variable changes inside the loop.

Since i is never increased, the condition i < 5 is always true, causing an infinite loop.

❓ Predict Output

advanced

While loop with break statement

What is the output of this MATLAB code?

MATLAB

i = 1;
while true
    disp(i)
    if i == 3
        break
    end
    i = i + 1;
end

A

1
2
3

B

1
2

C

1
2
3
4

D Infinite loop with no output

💡 Hint

The loop stops when i equals 3.

The loop prints i starting from 1. When i reaches 3, the break stops the loop, so output is 1, 2, 3.

🧠 Conceptual

expert

Number of iterations in nested while loops

How many times will the inner disp statement run in this MATLAB code?

MATLAB

i = 1;
count = 0;
while i <= 3
    j = 1;
    while j <= 2
        disp([i, j])
        count = count + 1;
        j = j + 1;
    end
    i = i + 1;
end

A 2

B 5

C 3

D 6

💡 Hint

Multiply the number of outer loop runs by inner loop runs.

Outer loop runs 3 times, inner loop runs 2 times each, so total is 3*2=6.

Practice

1. What does a while loop do in MATLAB?

easy

A. Repeats a block of code as long as a condition is true

B. Executes code only once

C. Runs code a fixed number of times

D. Stops the program immediately

Solution

1. Step 1: Understand the purpose of a while loop

   A while loop runs repeatedly while its condition remains true.

2. Step 2: Compare options with definition

   Only Repeats a block of code as long as a condition is true correctly describes this behavior.

3. Final Answer:

   Repeats a block of code as long as a condition is true -> Option A

4. Quick Check:

   While loop = repeat while true [OK]

Hint: While loops run while condition is true, not fixed times [OK]

Common Mistakes:

• Thinking while loops run a fixed number of times
• Confusing while with if statement
• Believing while loops run only once

2. Which of the following is the correct syntax for a while loop in MATLAB?

easy

A. while condition
statements
end

B. while (condition) {
statements
}

C. while condition:
statements
end

D. while condition do
statements
end

Solution

1. Step 1: Recall MATLAB while loop syntax

   MATLAB uses 'while condition' followed by statements and ends with 'end'.

2. Step 2: Check each option

   while condition statements end matches MATLAB syntax; others use syntax from other languages.

3. Final Answer:

   while condition\n statements\nend -> Option A

4. Quick Check:

   MATLAB uses 'end' to close loops [OK]

Hint: MATLAB while loops end with 'end', no braces [OK]

Common Mistakes:

• Using braces {} instead of 'end'
• Adding colons after condition
• Using 'do' keyword

3. What will be the output of this MATLAB code?

i = 1;
while i <= 3
  disp(i)
  i = i + 1;
end

medium

A. 1 2 3 4

B. 1 2 3

C. 1 2

D. Error: infinite loop

Solution

1. Step 1: Analyze loop condition and increments

   The loop runs while i is less than or equal to 3, starting at 1 and increasing by 1 each time.

2. Step 2: Trace output values

   Values displayed are 1, then 2, then 3. When i becomes 4, condition fails and loop stops.

3. Final Answer:

   1 2 3 -> Option B

4. Quick Check:

   Loop prints 1 to 3 [OK]

Hint: Increment loop variable to avoid infinite loop [OK]

Common Mistakes:

• Forgetting to increment i causing infinite loop
• Expecting output to include 4
• Confusing loop condition with < instead of <=

4. Identify the error in this MATLAB code snippet:

count = 5;
while count > 0
  disp(count)
end

medium

A. disp function cannot be used inside while

B. Incorrect while syntax

C. Missing increment or decrement inside the loop

D. Variable 'count' not initialized

Solution

1. Step 1: Check loop condition and body

   The loop condition is 'count > 0', but inside the loop count is never changed.

2. Step 2: Understand effect of missing update

   Without changing count, the condition stays true forever, causing an infinite loop.

3. Final Answer:

   Missing increment or decrement inside the loop -> Option C

4. Quick Check:

   Update loop variable to avoid infinite loop [OK]

Hint: Always update loop variable inside while loop [OK]

Common Mistakes:

• Forgetting to change loop variable
• Assuming disp causes error
• Thinking syntax is wrong

5. Write a MATLAB while loop that sums numbers from 1 to 10 and stores the result in total. Which code correctly does this?

hard

A. total = 0;
i = 1;
while i <= 10
total = total + i;
i = i - 1;
end

B. total = 0;
i = 1;
while i < 10
total = total + i;
end

C. total = 0;
for i = 1:10
total = total + i;
end

D. total = 0;
i = 1;
while i <= 10
total = total + i;
i = i + 1;
end

Solution

1. Step 1: Understand the goal and loop condition

   We want to add numbers 1 through 10 using a while loop that stops when i > 10.

2. Step 2: Check each option for correctness

   total = 0; i = 1; while i <= 10 total = total + i; i = i + 1; end initializes total and i, adds i to total, increments i, and stops at 10 correctly. total = 0; i = 1; while i < 10 total = total + i; end misses increment causing infinite loop. total = 0; for i = 1:10 total = total + i; end uses for loop, not while. total = 0; i = 1; while i <= 10 total = total + i; i = i - 1; end decrements i causing infinite loop.

3. Final Answer:

   total = 0;\ni = 1;\nwhile i <= 10\n total = total + i;\n i = i + 1;\nend -> Option D

4. Quick Check:

   Increment i to sum 1 to 10 [OK]

Hint: Increment loop variable to reach end condition [OK]

Common Mistakes:

• Forgetting to increment i
• Using for loop instead of while
• Decrementing i causing infinite loop